Many people develop back pain during the course of their life due to traumatic injury, disease, or genetic defect. Typically, the patients' intervertebral discs, which support the spine, are damaged, causing the discs to bulge or herniate. The disc bulge then impinges on the nerves of the spine and causes back pain. Surgeons often perform a discectomy to trim the disc bulge to alleviate back pain. However, the discectomy may structurally weaken the disc and often leads to subsequent structural failure of the disc due to wear and aging, once again causing impingement on the nerves of the spine and back pain. Surgical implantation of a medical implant device to structurally support and separate the vertebrae may become desirable to end debilitating back pain and allow patients to regain normal life activities.
One known device for promoting fusion between adjacent vertebrae is an expandable interbody device (IBD). Such devices are generally configured to be inserted into the intervertebral space in a compact configuration, and then are expanded to an expanded configuration to restore the adjacent vertebrae to a desired spacing and provide stability at the affected joint. Numerous mechanisms are known for expanding the lateral size of an expandable IBD. It is also known to provide an IBD with one or more openings in the top and bottom surfaces of the IBD for containing bone graft material to promote fusion between the vertebrae to stabilize the joint.
One disadvantage of known laterally expandable IBDs is that the lateral size may be too large for insertion into the intervertebral disc space from a variety of surgical approaches, limiting the versatility of the IBD. For example, some known expandable IBDs include opposing body portions that are connected via a pivot or rotary hinge at one end and are configured for insertion with the body portions side-by-side. Such a side-by-side configuration is less advantageous or too large for some surgical approaches that have an especially narrow insertion opening.
Another perceived shortfall of known laterally expandable IBDs is maintaining the IBD in the desired expanded position. Some known laterally expandable IBDs lack structure to keep the device from expanding further or retracting after being expanded initially by a surgeon. Because the intervertebral joint is subject to movement, it is desirable for the expandable IBD to be restricted from shifting from the desired expanded configuration after being positioned in the intervertebral space.
A further disadvantage of known expandable IBDs is that it is difficult or impossible to insert bone graft material into or adjacent the expandable IBD after the IBD has been inserted into the intervertebral space. While some expandable IBDs may be configured to hold bone graft material for promoting fusion, once the device is expanded, in some cases there may not be sufficient bone graft material to fill the bone graft cavity in the device such that sufficient bone graft material is kept in contact with the adjacent vertebral endplate to adequately promote bone ingrowth.